[PATCH 3.16.y-ckt 038/135] libata: allow sata_sil24 to opt-out of tag ordered submission

[Luis Henriques]

3.16.7-ckt6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams at intel.com>

commit 72dd299d5039a336493993dcc63413cf31d0e662 upstream.

Ronny reports: https://bugzilla.kernel.org/show_bug.cgi?id=87101
    "Since commit 8a4aeec8d "libata/ahci: accommodate tag ordered
    controllers" the access to the harddisk on the first SATA-port is
    failing on its first access. The access to the harddisk on the
    second port is working normal.

    When reverting the above commit, access to both harddisks is working
    fine again."

Maintain tag ordered submission as the default, but allow sata_sil24 to
continue with the old behavior.

Cc: Tejun Heo <tj at kernel.org>
Reported-by: Ronny Hegewald <Ronny.Hegewald at online.de>
Signed-off-by: Dan Williams <dan.j.williams at intel.com>
Signed-off-by: Tejun Heo <tj at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/ata/libata-core.c | 5 ++++-
 drivers/ata/sata_sil24.c  | 2 +-
 include/linux/libata.h    | 1 +
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index e7f30b59bc8b..e1ad6e53073d 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4806,7 +4806,10 @@ static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
 		return NULL;
 
 	for (i = 0, tag = ap->last_tag + 1; i < max_queue; i++, tag++) {
-		tag = tag < max_queue ? tag : 0;
+		if (ap->flags & ATA_FLAG_LOWTAG)
+			tag = i;
+		else
+			tag = tag < max_queue ? tag : 0;
 
 		/* the last tag is reserved for internal command. */
 		if (tag == ATA_TAG_INTERNAL)
diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index 0534890f118a..e5d4928bdd53 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -246,7 +246,7 @@ enum {
 	/* host flags */
 	SIL24_COMMON_FLAGS	= ATA_FLAG_SATA | ATA_FLAG_PIO_DMA |
 				  ATA_FLAG_NCQ | ATA_FLAG_ACPI_SATA |
-				  ATA_FLAG_AN | ATA_FLAG_PMP,
+				  ATA_FLAG_AN | ATA_FLAG_PMP | ATA_FLAG_LOWTAG,
 	SIL24_FLAG_PCIX_IRQ_WOC	= (1 << 24), /* IRQ loss errata on PCI-X */
 
 	IRQ_STAT_4PORTS		= 0xf,
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 92abb497ab14..622459aea211 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -230,6 +230,7 @@ enum {
 	ATA_FLAG_SW_ACTIVITY	= (1 << 22), /* driver supports sw activity
 					      * led */
 	ATA_FLAG_NO_DIPM	= (1 << 23), /* host not happy with DIPM */
+	ATA_FLAG_LOWTAG		= (1 << 24), /* host wants lowest available tag */
 
 	/* bits 24:31 of ap->flags are reserved for LLD specific flags */
 
-- 
2.1.4